Systems are known in the art which use thermocouples for flame detection in gas burners, particularly domestic gas burners such as cooktop and ovens.
If there is a flame, the thermocouple generates a potential difference and hence a current strength at the ends of the cold junction, and the two ends are generally connected to an inductor which creates a force that moves the magnet of the safety valve for turning on and shutting off the gas supply.
Users of common cooktops manually excite such magnet to turn on gas supply, by applying a force on the cooktop knobs, whereupon a flame is created, the thermocouple detects the flame and generates a current that keeps the safety valve open, and the user may stop exerting force.
If the flame is blown out, the thermocouple ceases to generate current and the safety valve closes, thereby cutting off the gas flow.
This system apparently can have low manufacturing costs and be easily implemented, but only affords one burner safety control, i.e. can only check whether a flame is present.
The voltage generated at the ends of the cold junction is dependent on the materials that form the thermocouple, but is never more than a few microvolts per Celsius degree. Thus, the generated voltage is too low to be read, unless advanced amplification systems and appropriate calibrations are used.
As a result, the implementation of checks and control functions other than the simple “on/off” safety check as described above on prior art thermocouple systems is still difficult and expensive.
This prevents thermocouple systems from being used in modern electrical appliances, particularly ovens, in which temperature control and timing are critical requirements.
Therefore, there is still the need for a thermocouple-based flame ignition and control system, that allows implementation of controls such as temperature and cooking time controls.